The present invention relates generally to pure metal powders and metal compound powders, and in particular to a new and useful method for producing submicron metal-containing particles in a liquid bath that can be used as is, or can be further processed for other industrial purposes. Such uses include, but are not limited to, slurries and pastes for electrochemical cells such as batteries, MLCCs (multi-layer ceramic capacitors) and other types of capacitors, and metal powders for battery materials, electronics, catalysis and magnetic materials.
In 1889, Mond and Langer discovered that nickel tetracarbonyl or Ni(CO)4, readily decomposes into essentially pure metallic nickel and carbon monoxide within the temperature range of about 150-315xc2x0 C. A major drawback of the Mond process is that nickel tetracarbonyl is a highly dangerous toxin. Similarly, carbon monoxide must be treated with extreme care. Accordingly, few organizations throughout the world employ this method.
The multi-layer capacitor paste market requires submicron (less than one micron) nickel powders with no agglomerated particles larger than about one micron in size.
Most commercial fine nickel powders are made by chemical vapor deposition (CVD), chloride reduction or aqueous precipitation. These technologies are very expensive to scale up, however.
The resultant nickel powders used by multi-layer capacitor manufacturers are initially sold as dry powders. The fine powders are subsequently dispersed into a liquid to form a slurry which is part of the paste making process. Manufacture of the paste adds a significant cost to the final product.
For decades, the assignee here decomposed nickel tetracarbonyl vapors in the gas phase to manufacture a variety of fine pure nickel powders. Extra-fine powders, with a primary particle size of less than about 0.5 microns, may be made by gas phase decomposition of the nickel carbonyl at temperatures above about 400xc2x0 C. Unfortunately, under these conditions, particle collisions create significant opportunities for sintering resulting in powders containing some undesirable particles that are in excess of one micron.
All current techniques for producing dispersions containing submicron particles require expensive multi-step batch operations to manufacture the desired slurries and pastes.
During the early development of nickel carbonyl technology around the turn of the last century, it was recognized that the passage of nickel carbonyl with hydrogen through a fluid resulted in the catalyzation and formation of organic compounds. See German patent 241,823 to Shukoff of 1911.
Similarly, U.S. Pat. No. 1,138,201 to Ellis teaches the hydrogenation of heated oils. The nickel carbonyl is utilized as a source of fine catalytic nickel within the oil. In both instances, the nickel particles are separated from the liquid leaving behind the hydrogenated compounds. Apparently there was no recognition that a subsequently treated liquid dispersion, such as a paste or slurry, with entrained nickel particles therein had any utility.
Also see C. Ellis, Hydrogenation of Organic Substrates Including Fats and Fuels, 3rd Ed, Van Nostrand, N.Y. 1930, pages 164-167 which discuss the Shukoff and Ellis patents.
U.S. Pat. Nos. 1,759,658 to Mittasch et al. and 1,759,661 to Muller et al. disclose techniques for producing finely divided metals using metal carbonyls.
U.S. Pat. No. 3,504,895 discloses a process for making metal powder from carbonyl by decomposing the carbonyl in a liquid environment and recycling the non-metal products.
U.S. Pat. No. 3,228,882 discloses a process for making cobalt powders by decomposing carbonyl in a solvent having a polymer therein for encapsulization.
U.S. Pat. No. 5,137,652 discloses a method for making metal nitrides in solution by introducing ammonia into a solvent consisting of an active agent and carbonyl.
U.S. Pat. No. 6,033,624 discloses a method for producing various metals and metal alloy powders by mixing a carbonyl precursor with an alloying element in a solvent.
E. Papirer, P. Horny, et al., xe2x80x9cThe Preparation of a Ferrofluid by Decomposition of Dicobalt Octacarbonylxe2x80x9d, Journal of Colloid and Interface Science, Vol. 94, No. 1, July 1983, pages 220-228, discloses a particle suspension of cobalt made by the thermal decomposition of toluene cobalt carbonyl in a solution with ethyl sodium sulfosulinatexe2x80x94a surfactant.
U.S. Pat. No. 4,808,216 to Kageyama et al. and U.S. Pat. No. 5,064,464 to Sawada et al. disclose the making of ultrafine magnetic metal powders by the gas-phase pyrolysis of metal carbonyl. No bubbling of a metal containing fluid through a liquid is taught or suggested.
U.S. Pat. No. 6,365,555 discloses a method of preparing metal containing compounds using hydrodynamic cavitation at elevated pressure. The effect of ultrasonic cavitation on nickel powders is also discussed in Suslick et al. xe2x80x9cHeterogeneous Sonocatalysis with Nickel Powder,xe2x80x9d J. of American Chem. Soc., 1987, Vol. 109, No. II, pages 3459-3461.
Although the cited references appear to teach the production of particles and/or colloids via liquid baths and some teach the decomposition of carbonyls using various methods, ingredients and techniques, they do not teach or suggest the present method of making a liquid dispersion with submicron metal-containing particles for pastes, slurries and other purposes.
There is a need for a continuous, cost-effective process that produces submicron metal or metal compound powders in liquid dispersions, thereby eliminating a number of intermediate processing steps.
The invention is a continuous low cost process for making a liquid dispersion of submicron sized particles of various pure metals or metal compounds.
Bubbles of a metal-containing fluid and carrier gas mixture are introduced in a liquid bath of selected composition and rheology. The bath is heated or otherwise exposed to predetermined conditions for decomposing the metal-containing fluid in the bath. The temperature that the bath is heated to varies depending on the desired properties of the particles produced, and the thermal characteristics of the liquid selected for the bath. As the bubbles rise, the metal-containing fluid decomposes into submicron metal or metal compound particles, without agglomerating while simultaneously dispersing throughout the liquid.
When nickel carbonyl vapor is the metal-containing fluid, the resultant nickel particles have an average diameter of about 0.1 microns which is an order of magnitude smaller than most current commercial nickel particles.
Accordingly, an object of the present invention is to provide a continuous method of manufacturing a liquid dispersion that includes submicron sized metal-containing particles, that comprises: establishing a bath of a selected liquid in a vessel; mixing at least one metal-containing fluid with a carrier gas to form a metal-containing fluid mixture, the metal-containing fluid being either a gas or liquid capable of decomposing under predetermined conditions in the selected liquid to form submicron sized metal-containing particles; bubbling the metal-containing fluid mixture through the selected liquid in the bath; and creating the predetermined conditions in the bath to cause at least some of the metal-containing fluid to decompose within the selected liquid in the bath to form the submicron sized metal-containing particles dispersed in the selected liquid, the selected liquid with dispersed particles having a selected rheology.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawing and descriptive matter in which preferred embodiments of the invention are illustrated.